In late April the Swiss ambassador to Tehran arrived in Washington with a secret message for the small team in charge of Barack Obama's outreach to Iran. The rulers in Tehran were getting ready to release the American journalist Roxana Saberi, who had been charged with spying. But they wanted the U.S. to know that if she was freed, it would not be a concession; it would be a test. For more than two years, U.S. forces in Iraq had been holding three Iranian diplomats they believed were members of Iran's Revolutionary Guards Corps, linked to terrorist attacks in the region....